1. Field of the Invention
This invention relates to the field of measuring and detecting systems utilizing ultra wideband (UWB) radar techniques. More particularly, the invention relates to methods and systems for reliably receiving and processing UWB electromagnetic pulses to determine the presence or the range of a target.
2. Background of Related Art
Ultra wideband (UWB) waveforms have been used in measuring and detecting systems and methods to attain extremely fine, sub-foot resolutions because of their extremely short (subnanosecond to a few nanoseconds) durations. With the advent of very high speed, high sensitivity detectors (see, for example, U.S. Pat. No. 5,901,172 in the name of inventors Fontana and Larrick, entitled ULTRA WIDEBAND RECEIVER WITH HIGH SPEED NOISE AND INTERFERENCE TRACKING THRESHOLD, incorporated herein by reference), the feasibility of such systems has been demonstrated.
UWB (also referred to as carrier-free, impulse, or baseband) waveforms have been proposed to determine the relative position of a target for ship docking (Ross, U.S. Pat. No. 4,510,496), for precision radar ranging for intrusion detection and alert systems (Woolfolk, U.S. Pat. No. 5,148,175), as speed and motion sensors (Mara, Nicolson and Ross, U.S. Pat. No. 4,152,701; McEwan, U.S. Pat. No. 5,361,070); for target range detection of slowly moving targets (Henning and Woolfolk, U.S. Pat. No. 5,049,887), for liquid level sensing (Rama and Robbins, U.S. Pat. No. 4,489,601), for buried mine detection, and many other purposes.
While originally described for communications applications, the high sensitivity, high-speed tunnel diode detector described in U.S. Pat. No. 5,901,172 can also be directly used in a UWB radar application. Specific advantages of this tunnel diode detector are its very high sensitivity and its high noise and interference immunity. The high sensitivity of the detector permits the application of low power (i.e., less than a few watts of peak pulse power) UWB radar to high resolution radar altimetry at altitudes exceeding 10,000 feet; and the detection of extremely low radar cross section (RCS) targets for such applications as suspended wire detection for helicopters and other manned and unmanned craft. High noise and interference immunity permits the co-location of a UWB radar sensor with other active onboard systems.
However, the minimum time to reset a single UWB detector element precludes the use of the detector for radar ranges less than approximately 50 feet (i.e., approximately 100 ns roundtrip delay). An application of the tunnel diode circuit of the present invention permits a significant reduction in the minimum achievable detection range to less than one foot. This minimum achievable range is attained without loss of the high sensitivity required for long range and low RCS applications. The reduction in minimum achievable range extends the applicability of the high sensitivity radar sensor to obstacle and collision avoidance for small unmanned vehicles, autonomous landing systems, intrusion detection, and a wide variety of other applications within the realm of knowledge of persons skilled in the art.